The long-term objective of this proposal is to understand the signaling mechanisms underlying desensitization of MOR1D-GRPR crosstalk, which is required for opioid-induced itch. Spinal or epidural opioid-induced itch is a prevalent side effect in pain management and the underlying molecular and cellular mechanisms are poorly understood. MOR1D, a Gi protein-coupled mu opioid receptor isoform, mediates morphine-induced itch through cross-activation of gastrin-releasing peptide receptor (GRPR), an itch-specific receptor in the spinal cord. This cross-talk leads to morphine-induced itch signaling We found that phosphorylation is a major mechanism underlying a rapid desensitization of MOR1D-GRPR signaling. In Aim 1, we will determine the effect of morphine-induced phosphorylation on MOR1D-GRPR signaling. Aim 2 will determine the function of GRK2/arrestin2 in MOR1D-GRPR desensitization. Aim 3 will examine the role of PKC in MOR1D-GRPR desensitization and test the hypothesis that PKC and GRK2/arrestin2 function independently. We will use a combination of mouse genetics, molecular, cellular, biochemical, biophysical, electrophysiological and behavioral approaches to address these questions. Our studies will improve understanding of the signaling mechanism underlying desensitization of MOR1D-GRPR, and may yield important information for novel therapeutics for treating opioid-induced itch without compromising opioid analgesia.